1. Field of the Invention
The present invention relates to digital phase modulators. More particularly, this invention pertains to a method for increasing the resolution of a digital phase modulator for a fiber-optic signal transmission or measuring device.
2. Description of the Prior Art
It is known to apply the same potentials to the electrodes of a phase modulator for driving purposes. The potentials, depending on their positions with respect to the light guiding path, effect a positive or negative shift in the light phase as the output of the modulator. (Electrodes are also referred to below as “positive” or “negative”).
Patent specification DE 197 53 427 C1 (Germany) discloses a method and a device for increasing the accuracy of a digital phase modulator constructed from binary weighted surface electrodes. Such a modulator may be employed in a fiber-optic signal transmission or measuring device (preferably a fiber-optic interferometer). In such a device, a less significant portion of a binary drive signal is fed via a digital/analog converter, with driver connected downstream, to a specific analog electrode of a digital phase modulator. Provision is made for storing correction values in a storage table that can be individually assigned to the electrodes of the phase modulator. In this way, manufacturing-related inaccuracies in phase modulation values can be corrected. Although the solution described in the cited patent document enables resolution to be increased, its technical complexity is comparatively high due, in part, to the use of correction tables, and in part to the need to employ a digital-to-analog converter with driver whose analog output values are of only limited thermal stability. Particularly when employed in fiber-optic gyroscopes (FOGs) having a closed control loop and other fiber-optic signal transmission and measuring devices, higher resolution without substantially larger substrate sizes is desired than has been previously achieved.